DMalone,
Now back to your original question. When we 'did' homeschool we used our travel as field trips,history assignments, writing assignments, lessons on navigation, astronomy, meteorology and math. Not sure what curriculum you will be using but we did a combination of self-directed learning and purchased curriculum, whatever you can certainly adapt your travels and use each as a unique learning experience. A visit to a Civil War battlefield, a museum all will be great experience. So any of your traveling experiences can be used as education. You might have him start a blog about life of a teen as a full timer.
A suggestion, at locations where you are staying Google 'homeschooling groups', I know there are plenty and most if not all are very welcoming.
Also, if he is interested in music or plays an instrument or wants to there is a great resource of video/dvd music lessons for just about any musical instrument he might want. http://www.homespuntapes.com/
Good luck, hope it's what you want it to be and hope this helps a little.
Sheila aka....